Before beginning your consideration of this region, it is vitally important
that you review the bones of the skull and mandible. This will orient you
to the region and help make understanding this very compact space more
clear. To complete the review which follows, you should read with skull
in hand and have pipe cleaners, dental floss threaders, cellophane tape,
and string available.

View the skull from the side; the so-called Norma lateralis. Identify
the bones which make up the lateral projection of the braincase. These
include the frontal, parietal, temporal, zygomatic, spheroid, and occipital
bones (fig. 1). On the lateral sides of the frontal, parietal, and temporal
bones are two curved lines, the temporal lined. These mark the attachments
of the components of the temporalis muscle to the skull. Anteriorly note
that the lines end at a vertical projection of the zygomatic bone, the
frontal process. Posteriorly the lower temporal line becomes continuous
with the zygomatic arch or cheer: bone . The space bounded by the temporal
lines, the zygomatic arch, and the frontal process of the zygomatic bone
is the temporal fossa. The main occupant of the temporal fossa is
the temporalis muscle. In addition to its attachment to the skull, the
temporaTis muscle attaches to the coronoid process of the mandible. Identify
the coronoid and condylar processes of the mandible. Try to imagine how
the large, semicircular temporalis muscle converges onto its tendon of
insertion on the coronoid process. Palpate your own temporalis muscle,
both at the posterior border of the frontal process of the zygomaiic bone
and just in front of your ear. By clenching your teeth you can observe
the jaw-closing functions of the different parts of this muscle.

The temporal fossa opens inferiorly into the infratemporal fossa.
To determine the extent and boundaries of the infratemporal fossa, a more
detailed analysis of the spheroid bone is required. The sphenoid is an
extraordinary bone which contains a body and, on each side of the body,
two wings and two pterygoid processes. The body can best be seen in the
interior of the cranium, where it houses the pituitary gland and is the
center of the middle cranial fossa (fig. 2). The lesser wings of
the spheroid are also seen there where they form most of the border between
the middle and anterior cranial fossae. The greater wings form part
of the lateral wall of the middle cranial fossa (fig. 2), and also part
of the temporal fossa (fig. I ). Projecting inferiorly from the greater
wings into the infratemporal fossa are the two pterv~oid processes.
These two processes can be most easily seen if the skull is viewed
from beneath after the mandible is removed (fig. 3). The large and flat
lateral pterygoid process or plate lies just posterior to the maxilla and
is roughly in line with the maxillary tooth row. The more slender medial
pterygoid process lies more medial and contains a small, medially directed
hook at its inferior extreme. the pterygoid hamulus. Identify the foremen
lacerum. Recall that in life, most of this foremen is covered with fibrocartilage
to form the carotid canal, which marks the passage of the internal carotid
artery into the skull. Note the close relationship between the foremen
and the pterygoid plates.

Just anterior to the lateral pterygoid plate, between it and the maxilla,
is the pterygomaxillary fissure (fig. 4). Look into the depths of
this fissure, either by holding the skull up to the light, or by using
a penlight, and observe that at its base is a fossa, the pterygopalatine
fossa, ana an opening, the sphenopalatine
foremen. Place a dental floss threader into the pterygomaxillary fissure
and guide it through the sphenopalatine foremen. Note that the floss threader
now lies in the nasal cavity. Between the two pterygoid plates is a small
depression, the scaphoid fossa, and at its anterior end is an opening to
a bony canal, the pterygoid canal. Pass a dental floss threader into this
canal and look into the pterygomaxillary fissure to confirm that the threader
passes into the sphenopalatine foremen. Find the greater palatine foremen
on the surface of the hard palate ( fig. 3). By passing a floss threader
into this foremen, confirm that it too communicates with the sphenopalatine
foremen. Find the foremen rotundum in the middle cranial fossa. Pass a
pipe cleaner through it and, turning the skull over, push the pipe cleaner
through the inferior orbital fissure into the orbit. Note that the pipe
cleaner, which follows the course of the maxillary nerve, passes directly
over the pterygopalatine fossa. If these observations are viewed another
way, the pterygopalatine fossa is a place where several pathways converge.
The sphenopalatine foremen, the pterygoid canal, greater palatine foremen,
and the inferior orbital fissure all communicate with it directly.

Once all of these bony landmarks have been found, the boundaries of
the infratemporal fossa can be easily delineated. Replace the mandible
and follow the description of the boundaries. The lateral wall is formed
by the ramus of the mandible. Near the center of this ramus note the mandibular
foremen. At the anterior end of the fossa the maxilla forms the boundary.
At the top of this anterior wall is the inferior orbital fissure. At the
medial extreme of the anterior wall is the pterygomaxillary fissure. The
medial wall of the infratemporal fossa is formed by the lateral pterygoid
plate. The roof of the fossa is mainly the temporal fossa, but note that
the infratemporal fossa is somewhat deeper than the temporal fossa so that
a small bony roof, formed mainly by the spheroid, can be identified. Two
important foramina lie m this roof: the foremen ovate and the foremen spinosum.

II. Contents of the Infratemporal Fossa

By now you should have a pretty good idea of the bony landmarks surrounding
and forming the infratemporal fossa and of the foramina opening into it.
Before proceeding to a dissection of the region, it will be useful to review
the contents of the infratemporal fossa, so that you can develop an idea
of what you should expect to find. The infratemporal fossa contains the
pterygoid muscles, the maxillary artery and its branches, the pterygoid
venous plexus, and branches of the mandibular division of the trigeminal
nerve. In addition, the maxillary division of the trigeminal nerve courses
in the roof of the fossa.

Pterygoid muscles

The pterygoid muscles are muscles of mastication. They arise from the
two sides of the lateral pterygoid plate and insert onto the mandible (fig.
5). The deeper and larger medial pterygoid muscle courses from the medial
side of the plate to the angle of the mandible. It acts to pull the mandible
up and forward during chewing. The lateral pterygoid courses from the lateral
side of the plate to the condylar process of the mandible. It has two heads.
The larger oblique head acts much as the medial pterygoid muscle. The smaller
horizontal head pulls the mandibular condyle forward during jaw opening.

Maxillary Artery

The main arterial supply to the infratemporal fossa is the maxillary
artery (fig. 6). This is the largest terminal branch of the external carotid
artery (the other terminal branch is the superficial temporal artery, which
supplies the contents of the temporal fossa). The maxillary artery arises
just posterior to the neck of the mandible in the substance of the parotid
gland and courses somewhat obliquely through the fossa to end in the pterygomaxillary
fissure. Through its course It usually lies lateral (superficially to the
lateral pterygoid muscle, but it can sometimes lie on the deep side of
the muscle. It has an impressive number of branches, but the important
ones can be learned with careful attention to the course of the artery.
Two early branches are the middle meningeal and the inferior alveolar.
The middle meningeal artery courses superiorly from the maxillary
and leaves the infratemporal fossa through the foremen spinosum, thereby
entering the middle cranial fossa, where it supplies the meninges. The
inferior alveolar artery courses inferiorly from the maxillary,
enters the mandibular foremen, and courses in the body of the mandible,
supplying the mandibular teeth. Numerous muscular branches leave the maxillary
artery during its course. Especially important among these are the deep
temporal artery which courses on the deep surface of the temporalis
muscle, and the buccal artery which supplies the cheek region. The
terminal branch of the maxillary artery is the sphenopalatine artery.
It enters the pterygomaxillary fissure and will penetrate the sphenopalatine
foremen to supply the soft palate and nasal regions. However, before leaving
the infratemporal fossa, it gives off branches to the upper molar teeth
(posterior superior alveolar), palate (descending palatine) and orbit (infraorbital).

Pterygoid Plexus

The veins corresponding to the branches of the maxillary artery form
a plexus on the lateral and medial surfaces of the lateral pterygoid muscle
called the pterygoid plexus (fig. 7). The pterygoid plexus communicates
directly with the internal jugular venous system, via the retromandibular
vein, but also with the facial vein, via a deep facial vein, with the cavernous
sinus of the skull via a small tributary coursing through the foremen ovate,
and with a plexus of veins on the pharynx via the sphenopalatine foremen.
You should keep in mind that all of these veins are valveless, so that
blood can flow in either direction in them, depending on the prevailing
pressure gradients.

Any time spent mastering the distribution of the maxillary artery will
be time well spent, since the distribution of the branches of the mandibular
division of the trigeminal nerve will be similar.

The mandibular division of the trigeminal nerve enters the infratemporal
fossa through the foremen ovate (fig. 8). Unlike the other divisions of
the trigeminal nerve, the mandibular division contains motor axons which
supply skeletal muscle. Branches of this division innervate the muscles
of mastication: the medial and lateral pterygoid muscles, the temporalis,
and the masseter, all via branches in the infratemporal fossa. In addition
the mandibular nerve innervates the mylohyoid muscle and the anterior belly
of the digastric muscle outside of the fossa.

Upon entering the infratemporal fossa, the mandibular nerve usually
forms anterior and posterior branches. The anterior branches include muscle
branches and the buccal nerve, an important source of SENSORY innervation
to the skin of the cheek. (Remember that the buccinator muscle receives
its motor innervation from buccal branches of the facial nerve.)

The posterior division of the mandibular nerve is chiefly sensory. There
are three main branches.

1. The auriculotemporal nerve arises as two roots that encircle
the middle meningeal artery. It courses posteriorly! in the infratemporal
fossa, deep to the lateral pterygoid muscle, and ascends just in front
of the ear, in the company of the superficial temporal artery. It provides
mainly sensory innervation to the scalp, although it also receives autonomic
axons from the otic ganglion destined for the parotid gland.

The otic ganglion lies at the top of the infratemporal fossa,
just below the foremen ovate, behind the medial pterygoid muscle, and just
anterior to the middle meningeal artery (fig. 9). Parasympathetic preganglionic
axons course to the otic ganglion from their source in the glossopharyngeal
nerve via the lesser petrosal nerve. The lesser petrosal nerve passes
through a canal in the temporal bone and emerges in the infratemporal fossa
in or near the foremen ovate. These axons synapse in the ganglion and postganglionic
axons join the auriculotemporal nerve to supply the parotid grand. In addition,
sympathetic postganglionic axons derived from the cells of the superior
cervical ganglion enter the otic ganglion from a plexus on the middle meningeal
artery. They course through the ganglion without synapsing, join the auriculotemporal
nerve' and supply blood vessels in the parotid gland.

2. The lingual nerve descends on the deep surface of the lateral
pterygoid muscle where it receives a small branch, the chorda tympani
nerve (fig. 8). The chorda tympani nerve arises as a branch of the
facial nerve in the petrous portion of the temporal bone. Instead of coursing
through the facial canal with the main part of the nerve, it courses through
a small canal in the temporal bone, through the middle ear cavity (hence
its name), and emerges from the skull at the posterior extreme of the infratemporal
fossa. It carries special sensory fibers associated with taste and parasympathetic
preganglionic axons destined for the submandibular ganglion. After receiving
this branch, the lingual nerve courses deep to the mucosa of the floor
of the mouth, passes beneath the duct of the submandibular gland and supplies
mainly sensory innervation to the anterior V3 of the tongue. These include
general sensation and special sensation associated with taste buds. In
addition, axons from the lingual nerve supply the submandibular ganglion.
Some of the parasympathetic postganglionic axons from submandibular ganglion
cells join the lingual nerve to supply glands in the mucous membrane of
the floor of the mouth.

3. The inferior alveolar nerve courses with the inferior alveolar
artery, enters the mandibular foremen and courses forward in the mandibular
canal, ending as it emerges anteriorly from the mental foremen as the mental
nerve. It supplies sensory innervation to the mandibular (lower) teeth
and gums and to the skin of the chin region. Just before entering the mandibular
foremen, the inferior alveolar nerve gives off a mylohyoid branch. This
branch courses inferiorly, along the inner-side of the mandible and supplies
the mylohyoid muscle and the anterior belly of the digastric muscle.

The maxillary division of the trigeminal nerve makes only a cameo appearance
in the infratemporal fossa. It courses through the roof of the fossa, leaving
the skull via the foremen rotundum and then entering the orbit through
the inferior orbital fissure. It terminates anteriorly as the infraorbital
nerve. Thus the maxillary nerve courses over the pterygopalatine fossa,
and communicates with it. The maxillary nerve has numerous sensory branches
to the face (infraorbital and zygomatic branches) and maxillary (upper)
teeth (anterior and posterior superior alveolar branches). It also contains
axons of sensory and autonomic neurons the lacrimal gland and the mucosa
of the palate and pharynx. These latter are not originally part of the
trigeminal nerve, but simply "hitch a ride" with it so that they deserve
special consideration.

Parasympathetic preganglionic axons derived from the facial nerve leave
the main trunk of the nerve and course in a special canal in the temporal
bone as the greater petrosal nerve (fig. 10). Sympathetic postganClionic
axons derived from cell bodies in the superior cervical ganglion course
on the surface of the internal carotid artery and enter the skull with
the artery at the carotid canal. Just before the internal carotid artery
enters the cavernous sinus. some of these axons leave to form the deep
petrosal nerve, course a short distance in the temporal bone, and join
with the greater petrosal nerve to form the nerve of the ptervgoid canal.
(Recall the proximity of the carotid canal and the opening of the pterygoid
canal from your examination of the base of the skull.) This mixed nerve
courses through the pterygoid canal to end in the sphenopalatine foremen.
The sympathetic axons course through the adjacent pterygopalatine ganglion
without synapsing and are distributed with the nerve and arterial branches
emanating from it, to the mucosa of the nasal and pharyngeal regions. The
parasympathetic fibers entering the pterygopalatine ganglion synapse there
and distribute to glands in the same mucous membranes. In addition, some
of the postganglionic axons pass to the lacrimal gland by way of first
the maxillary nerve, then one of its branches, the zygomatic nerve, and
finally by way of one of the branches of the ophthalmic division of the
trigeminal nerve, the lacrimal nerve (fig. 10). Sensory axons of the maxillary
division of the trigeminal nerve from the nasal, palatine, orbital, and
lacrimal regions take courses similar to these autonomic neurons (but in
the opposite direction) and pass through the pterygopalatine ganglion without
synapsing. Their cell bodies (equivalent to those found In the dorsal root
ganglia) lie in the trigeminal ganglion.

Plan for Dissection

By now you should be familiar with the boundaries and contents of the
infratemporal fossa, so that a detailed dissection plan will seem somewhat
silly. Your individual dissection plan should, as always, keep in mind
the structures that you wish to see as well as those structures you want
to preserve for your demonstration of the region. The instructions which
follow are only designed to be very general ones.

First, you will want to orient yourself to the region on your cadaver.
Find the palpable bony boundaries of the fossa: the zygomatic arch the
frontal process of the zygomatic bone, the angle of the mandible, and the
external acoustic meatus (alveolar), palate (descending palatine) and orbit
(infraorbital).

Identify the masseter and temporalis muscles and the coronoid and condylar
processes of the mandible. In order for you to expose the infratemporal
fossa, you will have to remove its lateral wall, the ramus of the mandible,
and the zygomatic arch. However, you will want to be especially careful
in doing so, as you will not want to destroy the contents of the fossa
in the process. The best way to insure success is to recall the superficial
structures of the fossa and to move them out of the way before you remove
the bone. The procedure described in your dissector is a good starting
point. Removal of the zygomatic arch, temporalis muscle, and the coronoid
process of the mandible should be done first. In removing the rest of the
mandibular ramus, don't spend too much time looking for the "lingula".
Your objective will be to make your saw cut above the level of the mandibular
foremen, so that the important inferior alveolar vessels and nerves will
be preserved. To do this, run the tip of a probe down the inside of the
mandible until you feel it catch in the mandibular foremen. Note the length
of the probe to the tip from the mandibular notch. Mark this distance on
the outside of the mandible and make the third saw cut above this line.
The third saw cut should be done especially carefully to preserve the lateral
pterygoid muscle and maxillary artery, both of which course close to the
suggested area. Once the infratemporal fossa is opened, identify the two
heads of the lateral pterygoid muscle and then cut its posterior connections
and reflect it forward. If this is not possible, then remove the lateral
pterygoid muscle in pieces, taking care not to damage arteries branching
off of the maxillary artery. Follow a similar procedure for removing or
reflecting the medial pterygoid muscle, so that the mandibular nerve can
be seen entering the infratemporal fossa through the foremen ovate. You
should now have a good idea of how and where to find most of the important
structures you want. If you are confused by what you see, review the contents
of the fossa with your dried skull, and try to relate what you see to what
you have learned on the skull.